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Data_Organization

Graphs of CERA-2 Module DATA_ORGANIZATION and Submodule PATCHED_DIMENSION


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Overview

In module DATA_ORGANIZATION information is stored on the form, in which time information and spatial information are represented in the data set, i.e., how is the data distributed in the four dimensional space-time.


The information can be given as weekly data on a three dimensional simple grid. In this case, data points are equally spaced in all four dimensions. On the other hand, measurements on an ascending balloon will result in irregular changes of at least the space coordinates. In between these two extremes any combination of regular and irregular distributed positions can be relevant for describing the data. Additionally, one has to allow for or projections, i.e. when the data has no extension along a certain dimension, e.g. surface data or data valid at one certain moment of time only.


For the storage in module DATA_ORGANIZATION the four dimensions x, y, z, and t have to be divided into gridlike and pointlike ones. The coordinate values of pointlike dimensions normally are only valid for one certain data point each, while values of gridlike dimensions are related to many points, that differ in at least one of the other coordinate values.


The structure of gridlike dimensions is described in tables Scale and Time. This structure is defined by a set of positions on each axis, that make up the grid. They are given in tables Position and (for the time dimension) Moment. The positions can be equidistant, irregular, or in case of a projection just a single point; so can be the dimensions, what is described by the table Dim_type for each dimension.


For pointlike dimensions the coordinate values of each point (having a number of coordinates equal to the number of pointlike dimensions to describe) are stored in tables Point and (for the time dimension) Moment, being combined in the Point_set. Remaining gridlike dimensions can be described as before.


The following examples are to clarify this.

 

Examples

Simple Grid

For a simple grid in space-time the three ?_scale_id variables in SPACE and the time_id in DATA_ORG point to the axis' descriptions in tables Scale and Time. There the number of points along each axis is defined as well as the type of the grid.

In case of irregularly gridded points along a certain dimension, the positions on the axis are given in Position or Moment, instead.

For regular grids, only the first and last point has to be entered into Position/Moment. Their difference divided by the number of points yields the grid's spacing. Alternatively, one can specify the starting point and step width. Together with the number of points they yield the end point. The latter form of storage is more convenient for continouusly extended datasets. The type of storage should be referenced in table Dimension_type.

Balloon

Aperiodic measurements on, e.g., a flying balloon lead to a set of points in space-time, that is described in Point_set. For every point the space coordinates x,y,z (table Point) as well as the time of measurement (table Moment) are given.
The sequence_no in Point_connect is necessary if the points are not ordered by time or if all measurement are taken at one time at different points (projection along time axis). However, the field sequence_no should be filled in anyway.

Ocean Stations

Imagine you have for a couple of not moving ocean measurement stations the water temperature given at surface, at 2m, 5m, and 10m depths. As the stations are spread over the area, you describe their x,y (LON, LAT) position in Point, where the altitude and its unit_id are set to 0 (zero). The point set is pointed to by the point_set_id in Space, while here x_scale_id and y_scale_id are set to 0 (zero). z_scale_id points to SCALE where the irregular depth grid is described, consisting of the four positions 0, -2, -5, -10, given in Position. If, e.g., all stations give data every day, the equidistant grid is given in Time.
Describing one moving station is very similar. Just, that time_id in DATA_ORG is set to 0 (zero) and moment_id in Point_connect points to the moment, a certain measurement at the point (defined in Point) has been taken.

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